I have this very coop! I've been waiting for someone to ask me about it! I have the exact one you picture here, that I ordered pre-made from Williams Sonoma (no building skills). I also did the same thing you are planning to do, and built an expansion onto the run that is a walk-in (there is a little connector hallway; pics below).
I have two large size hens, and the coop works quite well for them. They did need some help with the ramp at first, but eventually they figured it out and have been fine. Bantams might need a block under it to prop it up and make it less steep, plus maybe some more treads on it, since they are spaced kind of far apart.
The positioning of the windows has worked well for ventilation, and the inside of the coop has done a good job staying dry even in very heavy rain. I love the cedar; it is sturdy and rot resistant. I do plant stuff in the planter, and that has worked fine and been very pretty; the planter is built with this nice drain-out feature that sends water out past the run. But my birds are heavy and non-fliers, so they never go up there.
The way it is sold from W-S, it has fairly narrow dowels for roosting bars, which I might change if I were building it myself. The coop maker also used wire flooring, which I didn't like, so I put in pine boards over it. The one problem with that is that, because of the coop design (those vertical slats where the alternating ones are recessed), you end up with little gaps at the end of the floor where bedding can fall in, so I have to clean those out occasionally, but not a big deal.
The other thing I did was add another layer of hardware cloth to the big main door, just for extra security.
In a perfect world, I might prefer to have the ladder outside the coop, leading to the exterior run, rather than part of the floor because it makes the floor a little more complicated to clean - if, for example, they poo on the ladder, that's harder to clean up than if the floor were just solid and covered with shavings.
On balance, though, I really like it. I am a first-time chicken owner, and it did not create any of the problems for me (moisture, drafts, etc.) that other people sometimes have to deal with. Having it elevated also makes it easy to clean and collect eggs from. Also, if you live on a small suburban lot like I do, its attractiveness is helpful for keeping neighbors happy.